The present invention generally relates to a cooling water supply system and more particularly, relates to an uninterrupted water cooling system capable of supplying cooling water to a process machine during a power interruption and a method for using the uninterrupted sub-loop water cooling system.
In the fabrication of semiconductor devices, various fabrication processes must be conducted in various physical or chemical process machines. A great majority of semiconductor process machines requires a cooling capability such that the temperature of the process chamber can be suitably controlled. These fabrication machines include deposition chambers such as those used in chemical vapor deposition, physical vapor deposition and furnaces for growing silicon oxides.
In a semiconductor fabrication facility, the total cooling capacity of all make-up air units, recirculation air units, air coolers, ventilation units, and central and process utility systems is normally provided by a chilled water system. For instance, the dehumidification operation in a make-up air unit requires a 6xc2x0 to 10xc2x0 C. temperature change in order to remove the excess moisture from the air, while the temperature of a cooling coil employed in a recirculation air unit needs to be controlled above the dew point of 9xc2x0 C. in order to prevent moisture from condensing such that the humidity inside a clean room can be maintained at a constant level. In a usual practice, the cooling water supply is returned or mixed in order to retain a temperature at between 14xc2x0 and 18xc2x0 C.
A water chiller can be constructed of a condenser and an evaporator. In most water chillers use in a semiconductor fabrication facility, the chiller is operated by a water-cooled principle supplied by a cooling tower. Inside the cooling tower, a cooling water is sprayed downwardly to meet the uprising outside air drawn in by a fan mounted on top of the cooling tower. A small amount of water evaporates as the water travels through the cooling tower such that, since evaporation of water demands heat, heat is removed from the cooling water to reach the desirable low temperature. In order to keep the system continuously running, the evaporated cooling water must be replaced.
Conventionally, cooling water required for semiconductor fabrication equipment is taken from a chilled water system using a heat exchanger. The primary side of the process cooling water system is connected to a chilled water supply system, while the secondary side is designed as an open system to keep the water pressure in the cooling water return lines as low as possible. For certain process tools such as physical vapor deposition chambers, the low return cooling water pressure is essential for preventing water from leaking into the process chamber. In the open process cooling water system, the recirculating cooling water is returned to a holding tank that is frequently opened to the atmosphere. Level sensors are used in the water holding tank to ensure a supply of deionized water to be added to the tank for compensating water loss due to evaporation.
A conventional cooling water supply system for semiconductor fabrication machines is shown in FIG. 3 and in systems A, B and C in FIG. 1. A typical cooling water system is shown as system A in FIG. 1 and in FIG. 3. A cooling water supply 10 at a temperature of about 13xc2x0 C. is first fed into the process equipment 12 through a first conduit 14 and a first shut-off valve 16. The cooling water supply exits the process equipment 12 through conduit 18 and shut off valve 20 into a cooling water return line 22. FIG. 3 further shows that a plurality of shut-off valves 24 are further utilized with one installed to the cooling water inlet of each process machine 12. As shown in FIG. 3, a series of process machines 12 can be connected in series, or in parallel, for intaking cooling water from the same cooling water supply source, and furthermore, outputting cooling water to a factory cooling water return line 22.
Others have attempted to improve the basic cooling water system by adding either a heat exchanger, or a heat exchanger and a compressor to the cooling water system. This is shown in systems B and C in FIG. 1. In system B of FIG. 1, heat exchanger 26 is added to the cooling water system to further improve the temperature control of the cooling water. However, as shown in FIG. 2, System B suffers a significant loss in efficiency, i.e., the efficiency dropped to about 70%. In still another improvement to the basic cooling water system, as shown in System C of FIG. 1, both a heat exchanger 26 and a compressor 28 are utilized in a dual heat exchanger mode. In this variation, the temperature of the cooling water can be more accurately controlled, again at a significant loss in efficiency, i.e., only 60% as shown in FIG. 2.
None of the System A, System B or System C is capable of preventing the problem of cooling water lose during an electrical power interruption at a fabrication facility. When a power outage occurs, an emergency power generation system normally starts immediately to supply power. However, even when the emergency back-up power supply system is immediately put in operation, there is still a time delay of between 30 and 60 seconds in most fabrication facilities. During the short duration of time, the electrical motor that pumps cooling water to the process machines stops resulting in a temporary loss of temperature control in the process machine. The stopping of cooling water circulation to the process machine, and the resulting loss of temperature control can result in a serious loss in fabrication yield since most fabrication processes are sensitive to the process temperature.
It is therefore an object of the present invention to provide a water cooling system for semiconductor fabrication machines that does not have the drawbacks or shortcomings of the conventional water cooling systems.
It is another object of the present invention to provide an uninterrupted sub-loop water cooling system for supplying cooling water to a process machine during a temporary power interruption.
It is a further object of the present invention to provide an uninterrupted sub-loop water cooling system for supplying cooling water to a process machine by utilizing a buffer tank for cooling water storage and delivery during the power interruption.
It is another further object of the present invention to provide an uninterrupted sub-loop water cooling system for supplying cooling water to a process machine that can be operated at 95% efficiency while consuming low uninterrupted power.
It is still another object of the present invention to provide an uninterrupted sub-loop water cooling system for supplying cooling water to a process machine by utilizing a buffer tank, a pump means and a battery power back-up system for running the pump.
It is yet another object of the present invention to provide an uninterrupted sub-loop water cooling system for supplying cooling water to a process machine during a power interruption by utilizing a pump means for drawing cooling water from both a cooling water reservoir and a cooling water buffer tank during a power interruption.
It is still another further object of the present invention to provide a method for preventing an interruption of cooling water supply to a process machine that can be carried out by providing a buffer tank that stores a quantity of cooling water for feeding to a process machine during power interruption.
It is yet another further object of the present invention to provide a method for preventing an interruption of cooling water supply to a process machine by operating a pump powered by an uninterrupted battery power back-up system for circulating cooling water stored in a buffer tank.
In accordance with the present invention, an uninterrupted sub-loop water cooling system for supplying cooling water to a process machine during a power interruption and a method for utilizing the system are disclosed.
In a preferred embodiment, an uninterrupted sub-loop water cooling system for supplying cooling water to a process machine during a power interruption can be provided which includes a buffer tank for storing a quantity of cooling water equipped with an inlet and an outlet, the inlet is in fluid communication with a cooling water reservoir through a first conduit, the outlet is in fluid communication with a cooling water return through a second conduit, at least one pump means that has an inlet in fluid communication with the first conduit for drawing cooling water from both the cooling water reservoir and the buffer tank, and an outlet in fluid communication with a cooling water inlet on a process machine, a process machine that has a cooling water inlet and a cooling water outlet, the cooling water outlet is in fluid communication with a second conduit of the buffer tank, and an uninterrupted power supply for operating the at least one pump means to supply cooling water to the process machine during a power outage by forming a sub-loop water-cooling system wherein cooling water is drawn from the buffer tank through the first conduit to flow through the process machine and return to the buffer tank through the second conduit.
In the uninterrupted sub-loop water cooling system for supplying cooling water to a process machine during a power interruption, the first conduit and the second conduit each may include a shut-off valve. The buffer tank may have a capacity between about 40 liters and about 400 liters. The quantity of cooling water stored in the buffer tank may have a temperature of between about 12xc2x0 C. and about 18xc2x0 C. The at least one pump means may have a pumping capacity of not less than 300 liter per minute, or between about 100 liter per minute and about 1000 liter per minute. The at least one pump means may be a pump driven by a motor of at least 5 horsepower. The uninterrupted power supply may be a battery power system that is sufficient for operating the at least one pump means for at least 2 minutes. The inlet and the outlet of the at least one pump means each further includes a shut-off valve. The cooling water inlet and the cooling water outlet of the process machine each may further include a shut-off valve.
The present invention is further directed to a method for preventing an interruption of cooling water supply to a process machine which can be carried out by the operating steps of first providing a process machine that has a cooling water inlet and a cooling water outlet, providing a buffer tank storing a quantity of cooling water therein, the buffer tank is equipped with an inlet and an outlet, connecting the inlet of the buffer tank in fluid communication with a cooling water reservoir through a first conduit equipped with a first shut-off valve, connecting the outlet of the buffer tank in fluid communication with a cooling water return through a second conduit equipped with a second shut-off valve, and turning on a pump means connected in a passageway of the first conduit and drawing cooling water from the inlet of the buffer tank and delivering to the cooling water inlet of the process machine when a power outage is detected and when the first and second shut-off valves are closed, the cooling water flows through the process machine and exits through the cooling water outlet into the outlet of the buffer tank.
The method for preventing an interruption of cooling water supply to a process machine may further include the step of connecting an uninterrupted power supply to the pump means. The uninterrupted power supply may be a battery power system that is sufficient for operating the pump means for at least 2 minutes. The method may further include the step for filling the buffer tank with a quantity of cooling water between about 40 liters and about 400 liters. The method may further include the step of maintaining the quantity of cooling water in a buffer tank at a temperature of between about 12xc2x0 C. and about 18xc2x0 C., or the step of flowing the cooling water through the process machine at a flow rate between about 100 liter per minute and about 1000 liter per minute, or the step of driving the pump means by a motor of at least 5 horsepower. The method may further include the step of providing a shut-off valve to each of the cooling water inlet and the cooling water outlet on the process machine, or the step of controlling the operation of the pump means by a microprocessor, or the step of controlling the operation of the first and the second shut-off valves by a microprocessor.